1. Field of the Invention
The present invention relates to microwave ovens generating microwaves and, more particularly, to a microwave oven including an antenna for properly propagating microwaves oscillated by a magnetron, as separate from a magnetron antenna.
2. Description of the Background Art
Some of conventional microwave ovens include an emission antenna in a waveguide. The emission antenna is connected, in terms of microwaves, to a magnetron antenna protruding from a magnetron. The provision of such an emission antenna increases power supply efficiency of microwaves to a heating chamber in the microwave oven.
Further, some of the conventional microwave ovens include an antenna for diffusion (hereinafter referred to as a diffusion antenna) on the side of a heating chamber, in addition to the emission antenna. The diffusion antenna may include a plurality of metal pieces radially arranged about a magnetron antenna or rotatably arranged. The diffusion antenna is provided for efficiently and uniformly supplying microwaves to the heating chamber.
In the conventional microwave oven, however, the impedances of the magnetron and the heating chamber cannot be sufficiently matched by merely providing the emission antenna in the waveguide or the diffusion antenna on the side of the heating chamber. If the impedances of the magnetron and the heating chamber are not sufficiently matched, most of the microwaves oscillated by the magnetron would be reflected back to the magnetron rather than be supplied to the heating chamber. Thus, the conventional microwave oven is desired to efficiently heat food by supplying as many microwaves oscillated by the magnetron as possible to the heating chamber.
Further, conventionally, it is difficult to uniformly supply microwaves to the entire heating chamber when microwaves are supplied to the heating chamber from the magnetron. Namely, the microwaves are often supplied unevenly to the heating chamber. As a result, food cannot be efficiently heated.
Moreover, a plurality of antennas may cause electric discharge thereamong. In such a case, similarly, food cannot be heated efficiently because the microwaves are not properly supplied to the heating chamber.
If a metal piece which is rotated by air force is provided as an antenna on the side of the heating chamber, a hole for guiding the air for rotation of the metal piece is formed in the heating chamber or waveguide. In this case, a wire or the like may be inadvertently inserted into the hole. Thus, such a hole must be made as small as possible. However, if the hole is too small, the metal piece cannot be sufficiently rotated. In such a case, microwaves supplied from the magnetron cannot be sufficiently agitated. As a result, the problem associated with unevenness of the microwaves supplied to the heating chamber is not eliminated and food cannot be efficiently heated.
The present invention is made to solve the aforementioned problem. An object of the present invention is to provide a microwave oven capable of efficiently heating food.
Another object of the present invention is to reliably provide for matching the impedances of the magnetron and the heating chamber.
Still another object of the present invention is to supply microwaves uniformly to the heating chamber.
Another object of the present invention is to avoid electric discharge among antennas provided in addition to a magnetron antenna.
A microwave oven according to one aspect of the present invention includes: a heating chamber containing food; a magnetron for heating the food in the heating chamber; a waveguide connected to the heating chamber and the magnetron for guiding microwaves oscillated by the magnetron to the heating chamber; and a diffusion antenna for diffusing microwaves oscillated by the magnetron. The microwave oven of the present invention is characterized in that the diffusion antenna extends from inside the waveguide to the heating chamber.
According to the present invention, an antenna extends from inside the waveguide to the heating chamber.
This enables the impedances of the magnetron and the heating chamber to be more reliably matched. Thus, the microwave oven can efficiently heat food.
Preferably, the microwave oven of the present invention further includes an antenna rotating portion for rotating the diffusion antenna.
Thus, the microwaves oscillated by the magnetron can be uniformly supplied to the heating chamber. This prevents heat unevenness of the food in the heating chamber.
Preferably, in the microwave oven of the present invention, the antenna rotating portion rotates the diffusion antenna by air force. The waveguide has a hole for permitting the air enter the waveguide from the antenna rotating portion and further includes an air guide member for guiding the air from a fan to the waveguide. The waveguide member has a wall opposite the hole of the waveguide.
This enables the diffusion antenna to be efficiently rotated and a bar-like foreign matter such as a wire would not be inserted to the hole of the microwave oven.
Preferably, in the microwave oven of the present invention, an antenna supporting plate supported by the diffusion antenna and having a main surface is further provided. As the antenna rotating portion rotates the antenna supporting plate in a plane including a main surface of the antenna supporting plate, the diffusion antenna is rotated. The diffusion antenna has a surface which is parallel to the main surface of the antenna supporting plate.
According to the present invention, the diffusion antenna can be more stably rotated.
Preferably, the microwave oven of the present invention further includes an antenna supporting plate capable of supporting a plurality of diffusion antennas. The antenna supporting plate has notches in a region between adjacent diffusion antennas on the antenna supporting plate.
According to the present invention, the adjacent diffusion antennas can be electrically insulated, so that electric discharge therebetween can be avoided.
Preferably, the microwave oven of the present invention is provided with a magnetron antenna used by the magnetron to radiate microwaves. The diffusion antennas are arranged at prescribed intervals in a circumferential direction of the magnetron antenna.
As such, the diffusion antennas can reliably diffuse the emitted microwaves through the magnetron antenna. Thus, heat unevenness of the food in the heating chamber can be reliably prevented.
Preferably, in the microwave oven of the present invention, the diffusion antenna has a plurality of surfaces, at least one of which is in a plane not passing the center of the magnetron antenna.
Thus, the microwaves supplied through the diffusion antenna would not concentrate near the center of the magnetron antenna. Accordingly, the microwaves oscillated by the magnetron can be efficiently supplied to the heating chamber.
Preferably, in the microwave oven of the present invention, the diffusion antenna has an end which is parallel to an inner wall of the waveguide.
Thus, a propagation path for microwaves is formed between the diffusion antenna and the inner wall of the waveguide. Accordingly, the microwaves can be efficiently supplied to the heating chamber through the diffusion antenna.
A microwave oven according to another aspect of the present invention includes: a heating chamber containing food; a magnetron for heating the food in the heating chamber; a magnetron antenna for emitting microwaves; and an emission antenna provided at the periphery of the magnetron antenna. The microwave oven is characterized in that the emission antenna is asymmetric with respect to the magnetron antenna in a plane orthogonal to the propagation direction of the microwaves oscillated by the magnetron.
According to the present invention, a distribution of the microwaves supplied to the heating chamber can be varied by changing the shape of the emission antenna.
Thus, the distribution of the microwaves supplied to the heating chamber can be varied according to the mounting position of the magnetron to the heating chamber in the microwave oven, so that the food can be efficiently heated.
Preferably, the microwave oven of the present invention further includes a waveguide connected to the heating chamber and the magnetron for guiding the microwaves oscillated by the magnetron to the heating chamber. A minimum distance in space between the magnetron antenna and the waveguide, excluding objects for reflecting the microwaves, is at least 7 mm.
Thus, electric discharge can be avoided between the magnetron antenna and the waveguide. Accordingly, secure operation of the microwave oven is ensured.
Preferably, the microwave oven of the present invention further includes a diffusion antenna provided in the waveguide. The emission antenna and a metal piece are arranged to overlap with each other in a propagation direction of the microwaves oscillated by the magnetron.
As a result, the microwaves are more intensely coupled in the propagation path within the waveguide. Accordingly, in the microwave oven, the microwaves can be efficiently supplied to the heating chamber.
Preferably, in the microwave oven of the present invention, at least one of the emission antenna and the diffusion antenna does not have a surface perpendicular to the inner wall of the waveguide.
Thus, electric discharge from the emission antenna or the diffusion antenna to the waveguide due to concentration of electric field at the wall of the waveguide can be avoided.
Preferably, in the microwave oven of the present invention, the magnetron has a magnetron antenna for emitting the microwaves. The diffusion antenna further includes a plurality of metal pieces radially arranged about the magnetron antenna near portions where the emission antenna is opposite another diffusion antenna through the magnetron antenna.
Thus, current can be supplied to another diffusion antenna through the metal piece at the portion near the magnetron antenna of each diffusion antenna. Accordingly, concentration of electric field at the portion near the magnetron antenna of each diffusion antenna can be avoided, so that the microwaves can be efficiently supplied to the heating chamber through the diffusion antenna.
A microwave oven according to still another aspect of the present invention includes: a heating chamber containing food; a magnetron for heating the food in the heating chamber; and a diffusion antenna for diffusing microwaves oscillated by the magnetron. The microwave oven is characterized in that the magnetron has a magnetron antenna for emitting the microwaves, and the diffusion antenna includes a plurality of metal pieces radially arranged about the magnetron antenna and arranged near the portions where the diffusion antenna is opposite another diffusion antenna through the magnetron antenna.
According to the present invention, current can be supplied to another diffusion antenna through the metal piece at the portion near the magnetron antenna of each diffusion antenna.
Thus, concentration of electric field to the portion near the magnetron antenna of each diffusion antenna can be avoided, so that the microwaves can be efficiently supplied to the heating chamber through the diffusion antenna.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.